Explosive forming method and means



Jan.

FIG.2

Y J. 5. CORRAL ET AL EXPLOSIVE FORMING METHOD AND MEANS Filed Sept. 30,. 1966 INVENTORS JOSEPH S. CORRAL DONALD E. KRANTZ ikw x mr ATTORNEY Unitcd States Patent 3,423,977 EXPLOSIVE FORMING METHOD AND MEANS Joseph S. Corral, Costa Mesa, and Donald E. Krantz, Tustin, Calif., assignors to North American Rockwell Corporation, a corporation of Delaware Filed Sept. 30, 1966, Ser. No. 583,352 US. Cl. 72-56 Int. Cl. B21d 26/08 9 Claims ABSTRACT OF THE DISCLOSURE This invention concerns method and means for forming sheet metal parts of any size or shape and diverse metallic or alloy compositions in order to achieve a final part of different shape.

Although the inventive teachings disclosed herein have wide applicability in forming a variety of diverse shapes, the invention will be described for the sake of illustration in connection with large aluminum sheets as used for aircraft external surfaces, for example. It will be understood that the scope of the concept is not limited by any of the specific details used to explain the invention, except as determined by reference to the accompanying claims. Also, the several features of the inventive concept which separately contribute to the final overall result may be advantageously used individually as well as in the combinations claimed.

Many different manufacturing techniques are known to the prior art for deforming sheet metal parts by applying force thereto in an amount which exceeds the yield strength of the material in such parts, in order to produce permanent deformation whereby the part may be forced to assume a contour corresponding to a die work face. :Included in the known methods are various techniques for application of explosive force, usually by immersing the die into a water filled pit, positioning the workpiece over the die, and detonating an explosive charge to force the workpiece against the die work face. A principal disadvantage of the foregoing method is that the maximum size of workpiece that can be formed is limited by the dimensions of existing water pits, and the cost of build ing larger pits is prohibitive in many cases, especially where few parts are required to be formed.

Accordingly, it is a principal object of the invention in this case to form large sheet metal workpieces into different final shapes by application of explosive forces not requiring immersion of the workpiece in a container of water.

It is a further object in this case to provide improved method and means according to the above object wherein the final contour of the workpiece may be controlled within relatively narrow marginal limits.

It is another object in this case to provide method and means as set forth in the above objects characterized by improved ease and economy.

It is a further object in this case to provide method and means as set forth in the above objects characterized by greater rapidity in performing the deformation step and wherein any portion of a large part may be deformed without exposing the remaining portion of the workpiece to explosive force.

Other objects and advantages of the instant invention 3,423,977 Patented Jan. 28, 1969 will become apparent upon a close reading of the following detailed description of an illustrative embodiment of the inventive method and means, reference being bad to the accompanying drawings, wherein:

FIGURE 1 is a general perspective view of apparatus incorporating the inventive principles disclosed herein and operatively related to a workpiece to be formed by the inventive method disclosed herein,

FIGURE 2 shows the workpiece from FIGURE 1 in its final form after completion of the operation performed by the apparatus of FIGURE 1,

FIGURES 3, 4 and 5 are cross-sectional views taken along planes indicated by lines 33, 4-4 and 5-5 of FIGURE 2, respectively,

FIGURE 6 is a side elevational view, partly in cross section, of the apparatus of FIGURE 1 taken along line 6-6 as indicated in FIGURE 1, and

FIGURE 7 shows heating means for the die of FIG- URE 1.

With reference to the drawings described above, and particularly to FIGURE 1, it may be seen that the inventive apparatus in this case may include a base plate 10 of strong material such as steel to serve as a stable reference whereby explosive force during the forming operation will not more the apparatus supported by base plate 10 downfardly or misalign the same due to such movement. Alternatively, base plate 10 may be replaced by a slab of reinforced concrete or the like. Base plate 10 supports a forming die 12 which may be cast or molded from a ceramic or suitable alloy having the requisite strength under shock loads, or formed in any convenient manner using conventional materials. Forming die 12 has a workface 14 which may be of male or female type and is contoured according to the desired fin'al shape of the workpiece illustratively shown as metal sheet or slab 16 in FIGURE 1. Metal sheet 16 is illustratively shown as elongate in form such as characteristic of the upper surface of an airplane wing or the like, in connection with which deformation of the material forming workpiece 16 is necessary only in one portion of the total workpiece, the remaining portion 18 being supported by suitable means as shown at 20 and otherwise remaining unaffected by the forming operations discussed further below. Workface 14 of die 12 is provided with a shallow groove 22 adapted to enclose an area at least as large as the portion of workpiece 16 to be deformed. Groove 22 has a width and a depth appropriately sized to receive a generally cylindrical and flexible elongate sealing element 24 in nesting relationship with slight excess volume in the groove to allow for expansion of seal 24 when compressed into the groove. The portion of workpiece 16 comprising the area thereof to be deformed is placed over workface 22 and in substantially continuous contact with sealing element 24, and securely held in the stated relationship by any suitable holding means. Illustratively, the stated means may take the form of clamping screws 26 threadably mounted in brackets 28 whereby rotation of screws 26 forces a rigid metal or wood strip 30 or other convenient force distributing element downwardly against a peripheral edge portion of workpiece 16 to hold the workpiece firmly against a portion of the die workface 14, compressing sealing element 24 in the manner shown, for example, by FIGURE 6.

With the workpiece 16, thus mounted and supported so that the portion thereof to be deformed is properly aligned over workface 14 of forming die 12, a heavy protective blanket of material possessing suitable strength and flexibility is placed over workpiece 16 as shown by blanket 32 in FIGURES 1 and 6. Illustratively, blanket 32 may comprise rubber or a synthetic rubber compound for cold-forming operations, or asbestos composition of heat-insulating qualities in the case of hot-forming operations. Containing means for containing a quantity of shock-wave transmitting and force-distributing media such as water 33 are placed over blanket 32 and may comprise a rectangular box or other suitable shape formed from plywood, flexible plastic or other convenient and expendable nature such as wood container 34. Alternatively, container 34 may be reused for many forming operations if fabricated from such high strength material as steel or the like. If necessary, a suitable sealing compound or tape may be used to seal along the juncture where the lower edge of box 34 contacts with the surface of blanket 32 as indicated by reference numeral 36 in FIGURE 6. Moreover, sealing means in the form of tape 38 or the like serves to seal the outer periphery of blanket 32 to the adjacent surface of workpiece 16 as shown in FIG- URES 1 and 6. For hot forming operations, media 33 may take the form of powdered silica, or other particulate of heat-resistant properties.

Within box 34, support means of suitable form such as hooks 40 are provided in spaced relationship along the inner surfaces of box 34 to support a net 42 which may comprise an ordinary fishnet, which in turn supports a suitable explosive 44. Explosive 44 is preferably in the form of an elongate cord which is interwoven with the fishnet and supported thereby an appropriate standoff distance from the surface of workpiece 16 as required to apply the necessary explosive force in an amount and at the location required to deform that portion of the workpiece aligned with workface 14 of die 12. Suitable means are provided for connecting vacuum lines to exhaust all atmosphere from the area above and below workpiece 16, such as indicated by inner tube tire valve connection 46 mounted on blanket 32 as shown in FIG- URE 6, and passage 48 communicating the area under workpiece 16 with an external vacuum pump (not shown). Prior to the application of explosive force, all air is evacuated from above and below slab 16 by use of vacuum pumps connected to items 46 and 48.

From the above description of the novel apparatus in this case, it will be understood that detonation of explosive 44 applies shock load to workpiece 16 deforming the same downwardly into close uniform contact with workface 14 of die 12, primarily in that area of workpiece 16 which is encompassed by the sides of box 34. The portion of workpiece 16 not so enclosed is not affected by the force of explosive 44 during detonation thereof, whereby very large parts may be deformed in any portion thereof using the apparatus and method disclosed herein. Moreover, large workpieces may be progressively formed over their entire area by successive use of several boxes 34 to achieve deformation in local portions of the workpiece incrementally throughout its length. In the example discussed above and' shown by the drawings in this case, it may be seen that the apparatus thus disclosed may deform workpiece 16 to produce the shape shown by FIGURES 2 through 5, from which it may be seen that a change in the longitudinal cross-sectional configuration through workpiece 16 is achieved as shown particularly by FIGURE 3, and that the portions of workpiece 16 indicated by cross sections 44 and -5 may be fiat or curved as seen from FIGURES 4 and 5, respectively.

From the description set forth above, it will be understood that the relatively shallow water container 34 provides the necessary medium for transmission of explosive energy shock waves in any portion of a large workpiece quickly, easily and inexpensively, thus avoiding the necessity of large pits or tanks as required to permit complete immersion of workpiece 16. Moreover, the use of net 42 and a matted explosive charge 44 in conjunction therewith permits close control of the amount of explosive force applied to the workpiece in localized areas as achieved by increasing or reducing the amount of explosive in any desired area of the workpiece.

Moreover, it will be further understood that blanket 32 forms a wall portion of enclosure means 34 and functions to confine media 33. Thus, blanket 32 is of particular value when media 33 is in liquid form. However, when media 3-3 is of dry particulate form such as sand, flour or powdered silica or the like, the protective qualities of such media and lesser tendency to leak through narrow gaps may make it feasible in a particular case to dispense with blanket 32. In addition, when hot-forming is done by the method and apparatus disclosed herein, workpiece 16 may be preheated or may be heated and maintained at an elevated temperature while supported over die 12 by use of a plurality of Inconel electrical resistance strips laid across the die workface, the workpiece itself, or embedded in die 12 close to workface 14, and connected with a suitable source of electrical power, all as suggested generally by FIGURE 7.

While the particular details set forth above and in the drawings are fully capable of attaining the objects and providing the advantages herein stated, the structure and method thus disclosed are merely illustrative and could be varied or modified to produce the same results without departing from the scope of the inventive concept as defined in the appended claims.

We claim:

1. In a method for forming a portion of a massive workpiece by application of explosive force thereto to said portion while the remainder of said workpiece is exposed to atmosphere and is unaffected by said force:

supporting said massive workpiece in a stationary state in air with said workpiece portion aligned with an underlying die workface,

placing an expendable enclosure on said workpiece portion aligned substantially over said underlying die workface and with said enclosure supported by said workpiece,

supporting an explosive charge within said expendable enclosure over an area generally corresponding to and in substantial alignment with said workpiece portion at a predetermined standoff distance from said workpiece,

filling said enclosure with force transmitting media in an amount suflicient to transmit and distribute said explosive force over said workpiece portion, said remainder of said workpiece being outside the limits of said enclosure, and

detonating said charge to produce said explosive force against said workpiece portion and deform the same against said underlying die workface.

2. The method set forth in claim 1 above, wherein:

said upstanding wall portion contacting said workpiece defines a surface area on said workpiece substantially coinciding with said workpiece portion, and

said supporting of said explosive charge is accomplished by distributing said explosive charge over an area substantially corresponding with said surface area.

3. The method set forth in claim 2 above, wherein:

said supporting of said explosive charge is accomplished by the steps of Weaving an elongate explosive material through a net and stretching said net over said surface area, and engaging a peripheral portion of said net with a plurality of supporting projections on said upstanding wall portion.

4. The method set forth in claim 1 above, wherein:

said enclosure is placed on said workpiece by the step of joining a plurality of wooden boards in mutual endwise contact to form a container defining a size and shape corresponding to said deformed workpiece portion and said underlying die workface.

5. The method set forth in claim 1 above, further including:

placing a sheet of flexible material in substantially uniform area contact with said workpiece over said workpiece portion, whereby said enclosure contacts said sheet.

6. The method set forth in claim 1, further including:

the step of evacuating the area between said workpiece and said underlying die Workface prior to said detonating step, and

clamping said workpiece to said underlying die Workface at the periphery thereof and in sealing relationship therewith prior to said evacuating step.

7. A method of progressively deforming a sheet of workpiece material by applying explosive force thereto, comprising the steps of:

supporting said workpiece in a stationary state with a first portion of said sheet overlying a die workface, covering said first portion of said sheet with a flexible protective blanket, placing container means on said blanket and in supported relationship with said workpiece first portion,

supporting an explosive charge in said container and in spaced relationship with said workpiece first portion,

placing force transmitting media in said container and in an amount sufficient to cover said explosive charge,

detonating said charge to deform said first portion into conformity with said die workface, and

repeating all said steps using a second portion of said sheet to deform said second portion in the same manner as said first portion.

8. The method set forth in claim 7 above, wherein:

said container means is formed by the step of draping flexible plastic sheets over upstanding support means so that said plastic sheets support said media in substantial alignment with said underlying die workface.

9. The method set forth in claim 1 above, wherein:

said enclosure is formed by the step of draping flexible plastic sheets over upstanding support means so that said plastic sheets support said media in substantial alignment with said underlying die workface.

References Cited UNITED STATES PATENTS 3,068,822 12/1962 Orr et al 72-56 3,128,732 4/1964 Paynter et a1. 72-56 3,175,618 3/1965 Lang et a1 72-56 3,222,902 12/1965 Brejcha et al. 72-56 3,224,238 12/ 1965 Henriksen 27-56 3,238,753 3/1966 Benatar et al. 72-56 3,267,780 8/1966 Roth 72-56 X 3,339,387 9/1967 Myers 72-63 FOREIGN PATENTS 1,236,074 6/ 1960 France.

RICHARD J. HERBST, Primary Examiner. 

